Monthly water temperature data from routine observations by research vessels, which are not conducted on the same day every year, includes not only interannual but also seasonal variations. In this study, using the monthly observation data for Osaka Bay from 1981 to 2010, we calculated continuous normal water temperature by interpolating between observations and normalized the anomalies. Normal temperature was expressed as a finite Fourier series, which had extreme values in mid-to-late

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... and August, and its phase difference from normal values of solar radiation and air temperature in Osaka was estimated at about 57 and 20 days. Time series of the anomalies exhibited no significant linear trend, but showed a significant upward shift in November 1993. Fisheries statistics suggested this temperature shift could affect fishery catches of some cold-water and warm water fishes.